It is hard to believe. But the presidential election process has begun in earnest. Two major candidates have recently announced they are running: Rand Paul and Hillary Clinton. And now Marco Rubio. Anything can happen, and in American presidential elections it often does. But these three, presumably along with Jeb Bush, are likely to comprise the field’s main contenders in the months ahead.

When foreigners look at America, they tend to focus on the continuities in US foreign policy. Critics tend to point out that America fights more wars than any other country and that presidents focus on promoting democracy and free trade, regardless of who is in office. American policymakers regard that as acting responsibly. Critics call it interference and, often, bullying.

But, after over a decade of war in the Middle East, many Americans are weary of its costs in terms of both blood and treasure. They want to invest money at home and shut out the world’s problems, if at all possible.

And so the run up to next year’s election promises to involve more than the usual amount of debate about how America should engage the world.

These three candidates – Clinton, Paul and Rubio – represent a stark contrast on that question.

Rand Paul: Keep them home

At one end of the spectrum is Rand Paul.

He is a devout opponent of the view that he believes has dominated foreign policy since the end of the Cold War: that America is the “indispensable nation” with an avowed duty to act as the “world’s policeman.”

Indeed, as he said in his 2011 book, The Tea Party Goes to Washington, the US is exceptional but that does not mean it has an exceptional mission to police the globe. Making the world safe for democracy, he suggested on page 153, is not an American foreign policy, let alone a conservative one. Indeed, he argued that the logic behind the 2003 invasion of Iraq was progressive left wing ideology – a claim that no doubt amuses George W Bush and Dick Cheney.

Paul’s position is conventionally associated with isolationism and historically, isolationism has unsavory connotations. This is because many conservatives favored non-intervention in the Second World War, right up until Japan’s bombing of Pearl Harbor.

The logic of isolationists is quite simple. The US is uniquely secure because of it great military prowess; the huge oceans to its east and west that separate it from its enemies; its friendly and militarily weak neighbors to the north and south; and its abundant resources. This last point is now magnified by the US’s new found energy independence.

So why, Paul asks, should the US get involved in wars from which the American people gain little and for which pay a large price? Why fight when our security is not really at stake?

Isolationists want to cut military spending with one exception: anything to do with border control. And here Paul is no exception.

In modern times isolationists focus on stopping the flow of anything they regard as insidious into the US – like drugs and terrorists, and illegal immigrants who “take our jobs.” So when Paul vowed, “to take our country back” in the speech announcing his candidacy, he deliberately and self-consciously left the precise meaning unclear. Was his target, as he suggested, “big government” or was it racial minorities or illegal migrants?

Paul is often testy when asked about such issues. He has clearly tried to retreat from his well-publicized isolationist remarks over Iran, Iraq and Israel in an attempt to appeal to more moderate Republican voters. He would rather talk about Hillary Clinton andBenghazi than seeming contradictions in his own position. But what is clear is that a Paul presidency would entail less military expenditure, fewer overseas commitments and even more money being spent on border security.

It’s a world that many foreign critics of the US might enjoy.

Clinton: Balancing ‘smart power’

Hillary Clinton has already suggested that she will focus her campaign on domestic rather than foreign policy issues.

The early signs are that she believes the adage that “it’s the economy, stupid” still applies. But nonetheless she is likely to be drawn into foreign policy debates during the campaign. And, as former Secretary of State, she has the virtue of having more foreign policy experience than any other candidate – Democrat or Republican.

If the past is any guide to the future, Clinton’s foreign policy approach will be a bridge between the kind of aggressive overseas adventures of George W Bush and the more restrained approach of Barack Obama.

In a 2014 interview, Clinton implicitly criticized Obama’s apparent lack of a grand strategy. In responding to Obama’s reputed comment that the first principle of foreign policy was not to do “stupid shit,” Clinton said at the time that, “Great nations need organizing principles, and ‘Don’t do stupid stuff’ is not an organizing principle.”

So what is her foreign policy approach likely to be? Well, in a 2010 piece in Foreign Affairs Clinton stated,

“I began my tenure as US Secretary of State by stressing the need to elevate diplomacy and development alongside defense – a ‘smart’ power approach to solving global problems. To make that approach succeed, however, US civilian power must be strengthened and amplified.”

The concept of “smart power” refers to the combination of “hard” military power and “soft” cultural power (like Hollywood).

We are likely to see that approach in a Hillary Clinton presidency.

It will be an America that is fully engaged in global affairs. One that is committed to multilateral coalition building, leading as a “first among equals.” But one that is focused on a greater balance between military power, diplomacy and aid.

America would certainly enlarge its foreign service – the heart of its diplomatic corps. And where Rand Paul would cut aid, Clinton would likely increase it.

Traditional allies in Europe, Asia and the Middle East would probably be reassured about the strength of Clinton’s commitment. And some of its enemies might even be beguiled by her focus on diplomacy, a focus that they have become accustomed to during the Obama administration.

Marco Rubio: Back to the future

Marco Rubio strikes a notable contrast with both Paul and Clinton.

Rubio has only been a senator since 2010. But he has sat on the Senate’s Foreign Relations Committee and amassed significant knowledge, if not experience.

Of these three candidates, by his own admission, Rubio offersthe most “muscular” option in terms of prospective foreign policy.

In a major 2012 speech at the Brooking Institution he may have openly extolled the virtues of multilateral coalition building. But his version of coalitions are ones forcefully instigated and led by the United States, ones that in practice look more like Iraq’s “coalition of the willing” (American unilateralism plus a few symbolic partners) than Obama’s “leading from behind” in which the US supports a coalition led by others.

Rubio’s core message is “peace through strength.” Given this context, he is predictable on the issues.

He criticizes Obama (and by implication Clinton in her then position of Secretary of State) on not being forceful enough in Libya, Syria and now Iraq. Rubio’s positions on China have been aggressive on economic issues and he has been a stout advocate of democracy-promotion in Latin America.

Not surprisingly, given his Cuban heritage, he is a proponent of immigration reform. But Rubio has been a blistering critic of Obama’s ongoing rapprochement with Cuba. Indeed, he called the policy shift “an illusion, based on a lie.” Critically, his position on Cuba distinguishes him, from both Clinton and his fellow Republican Paul.

So, these three differ significantly – in strategy, tone, policy style and on some of the most important issues, stretching from our own hemisphere to Europe, Asia and beyond. Other announced candidates, like Ted Cruz, or likely ones, like Jeb Bush, largely reflect the variation portrayed by them.

All this, and we haven’t even got to the first debate yet.

For once, it appears, those critics who point to a continued consensus in US foreign policy might find a puzzling road ahead